Graphing the Voice of Terror

Courtesy of Owl Investigations, Photography by John B. Carnett BIN LADEN, THROUGH THE NOISE, THREATENING MORE OF THE SAME
The bottom spectrogram is a clean bin Laden sample taken from an ABC News interview. Note the distinct vocal formants and their harmonics arcing right-to-left across the page. The top graph is of the dirty November telephone recording, in which formants are obscured by background noise -- so obscured, Tom Owen says, that no computer could ID the voice. Courtesy of Owl Investigations, Photography by John B. Carnett

Last November's split verdict on the Osama bin Laden tape was more than another disagreement between the United States and Europeans over the al Qaeda threat. It was a salvo in a war that is heating up over the future of forensic voice analysis, or voiceprinting.



On November 12, the independent Arabic station al Jazeera broadcast a recording of a call it claimed to have received from bin Laden, in which the al Qaeda leader praised recent terrorist attacks and promised more of the same. The CIA and National Security Agency immediately turned to their voice analysts. We don't know exactly what tools the top-secret NSA brought to bear, but it's very likely the agency's experts were, like their peers in the private sector, trained to parse speech by comparing spectrograms, a kind of graphic speech rendering that has changed little since the 1940s. Picture scratchy inkblots etched across a ribbon of paper and you have an idea what they were poring over.



The television networks turned to independent but agency-connected experts for their own judgment: Was this tape real? Within days, the verdict was in: bin Laden, alive and plotting.



Across the sea, Switzerland's IDIAP (Dalle Molle Institute for Perceptual Artificial Intelligence) turned to biometric software to analyze the tape. The institute's computers boiled the problem down to a shiny turquoise data point on the "non bin Laden" side of an algorithmically derived decision boundary. The Swiss analysis came with the qualifier that the study was motivated by "pure scientific curiosity, to . . . see what conclusion our state-of-the-art speaker authentication system would reach." The Swiss biometrics program put the likelihood of the voice being that of a bin Laden impostor at 55 to 60 percent. Equivocal at best, but enough to throw cold water on the American verdict, and by implication on traditional methods of forensic voice identification.



Back in the New World, the Old School wasn't impressed.



To show me why, Tom Owen, one
of North America's busiest forensic voice analysts -- and one of only eight certified by the American Board of Recorded Evidence -- invited me to his basement sound lab in Colonia, New Jersey. It was Owen who the major U.S. television networks turned to for verification of the government claim about the bin Laden tapes. On the afternoon of my visit, Owen had just finished teaching a month-long class in voice identification for a group of Saudi intelligence officers. Conveniently, a captain of the Saudi Interior Ministry's forensics department had been on hand when Owen received the bin Laden tape for analysis last November. Translation was not a problem.



A former audio engineer for New York's Lincoln Center, Owen fell into forensics in the 1980s, when an NYPD detective showed up at his sound studio with a "dirty" recording of a bomb threat. Owen cleaned up the background noise, as he had on countless old recordings of singers from Enrico Caruso to Dionne Warwick. It gave him a taste for forensic work.



Floor-to-ceiling racks of spectrum analyzers, signal processors, equalizers, mixers, amplifiers and record-playback systems wrap around the walls of Owen's soundproof basement. But as is often the case in forensics, the master's favorite tool remains a piece of vintage equipment -- a reel-to-reel Voice Identification 700 spectrograph built in 1973. It differs little from the analog machines U.S. Army intelligence officers built to identify and track German radio operators during World War II.